Impact of a DNase I and Vancomycin Drug Combination against a Mature Methicillin Resistant <i>Staphylococcus aureus</i> (MRSA) <i>in vitro</i> Biofilm

1.1 Abstract Antimicrobial resistant infections present a concerning and expanding healthcare problem that is compounded by the reduction of antimicrobial research by the pharmaceutical industry. Additionally, the currently used antimicrobials consistently present less than ideal clinical treatment outcomes. This contention is supported by in vitro analysis in appropriate models. Here, in mature methicillin resistant Staphylococcus aureus (MRSA) in vitro cultures, we tested multiple antimicrobials and showed that for a biofilm grown for 72 hours, no antimicrobial tested was able to completely eradicate the biofilm even after 24 hours of exposure. However, the addition of an enzymatic biofilm-dispersal agent (DNase I or Proteinase K), greatly improved the performance of vancomycin and tigecycline in this in vitro model. Despite the improved performance in the presence of the dispersal agent, a high concentration of antimicrobial, 2000 µg/mL, was needed to completely eradicate the infection as demonstrated by analyses using both a traditional XTT assay as well as a subculture assay to account for persister cells. It was shown that the addition of DNase I improved the diffusion of vancomycin through the biofilm. This suggests vancomycin efficacy is limited by the biofilm. The presented work provides a potential avenue for future treatments of MRSA lung infections by utilizing a traditional antibiotic combined with a passive dispersive agent.